Various hybrid vehicles have been designed and developed in the automotive industry that operate using fuel cell technology and other rechargeable energy storage and generating systems. In a typical fuel cell vehicle, a fuel cell generates electricity through an electrochemical reaction between hydrogen and oxygen to charge batteries or to provide power for an electric motor. In certain fuel cell vehicles, the vehicle requirements allow a higher power split between a battery system and a fuel cell system. In other words, the fuel cell system is the main energy source having a greater ratio of use than the battery system. The battery system covers peak loads, for example during acceleration, smoothens the fuel cell system load profile to enhance fuel cell system durability, and provides high voltage power in situations where the fuel cell system is not capable of producing power itself such as during startup and shutdown, for example. To support the fuel cell system in these vehicles, the vehicles are equipped with a high power density battery system.
The fuel cell vehicles equipped with the high power density battery system require a ventilation system for the battery system to control a temperature and maintain a performance of the battery cells. Performance of the battery cells is required for full vehicle performance including maximum acceleration and regeneration of kinetic energy during braking. The ventilation system for the battery system is separate from a cooling device controlling a temperature of the fuel cell system, as the temperature set points of the battery system and the fuel cell system are different.
Typically, the ventilation system includes a ventilator fan and a housing, and draws air from the passenger compartment of the vehicle. The air flows through a conduit to the battery system. However, passengers are exposed to noise generated by the ventilator fan and to the air being drawn into the conduit. Moreover, the extraction of air from the passenger compartment by the ventilation system may disrupt circulation of air in the passenger compartment, making it uncomfortable for the passengers in close proximity to the opening. Further, if the mass flow of the air drawn into the ventilation system is greater than the mass flow of the air being emitted by the HVAC system, the air may be drawn back through at least one HVAC system emission outlet into the passenger compartment to equalize the pressure in the passenger compartment, or, if a check valve is installed in the HVAC system emission outlets, the passenger compartment may become under-pressurized creating an uncomfortable environment for the passengers.
U.S. Pat. No. 6,978,855 discloses a cooling system for an electricity storing device in a fuel cell vehicle. The cooling system consists of a plurality of holes formed in the floor of the passenger compartment of the vehicle and a fan. The through holes are provided as inlet ports and outlet ports for a housing of the electricity storing device. The fan is disposed adjacent the inlet ports as a means for discharging air within the housing of the electricity storing device. Air flows into the housing through the inlet ports from the passenger compartment to cool the electricity storing device and is then discharged through the outlet ports into a space under a rear seat in the passenger compartment. Although the outlet ports are disposed at angles to prevent discharged air from directly entering the inlet ports, a temperature of the air drawn into the cooling system is influenced by the discharged air, making the cooling system less efficient. Further, the plurality of holes formed in the floor of the passenger compartment expose the passengers in the passenger compartment to the noise generated by the fan and the air discharged from the housing, thereby decreasing passenger comfort and perceived vehicle quality.
It would be desirable to develop a method for controlling ventilation of a rechargeable energy storage system (RESS) in a fuel cell vehicle, which prevents damage to or a shortened life of the energy storage device, while maximizing durability, efficiency, performance, and passenger comfort.